The present invention relates generally to the storage of data on magnetic recording tape, and in particular, to the storage of data on magnetic tape in cartridge form.
In the course of developing various systems for the storage of data on magnetic recording tape, particularly off-line storage of data in the form of back-up storage, a variety of different formats have been developed. Many of these formats call for the tape to be contained in an appropriate cartridge, both to facilitate handling of the tape while in use, and to protect the tape while in storage.
To this end, the IBM Corporation has developed a tape cartridge which is primarily intended for use in its Model 3480 data storage system, for the storage of relatively large quantities of data (on the order of 200 megabytes). Details regarding the construction of this type of tape cartridge (hereinafter referred to as a 3480 tape cartridge) may be had with reference to U.S. Pat. No. 4,452,406. By way of general description, the 3480 tape cartridge is comprised of a single reel containing a quantity of magnetic tape and contained in a rectangular enclosure having dimensions on the order of 4 inches in width, 5 inches in length, and 1 inch in height. The cartridge enclosure includes an aperture in one of its major faces, to receive means for rotating the reel of tape contained within the cartridge, and an aperture in one of its corners, for gaining access to the free end of the web of tape. A so-called "leader block" is connected to the free end of the tape, and is retained within the open corner of the cartridge so that it is capable of being withdrawn from and replaced within the cartridge by appropriate means.
In connection with the 3480 tape cartridge, IBM Corporation has also developed equipment for receiving the tape cartridge and for properly placing the web of tape which it contains in operative association with a magnetic read/write head. Further details regarding such equipment may be had with reference to U.S. Pat. Nos. 4,432,508; 4,399,959; 4,399,936; and 4,335,858, which illustrate various different devices which have been developed by the IBM Corporation to accommodate its 3480 tape cartridge.
The 3480 tape cartridge has found wide acceptance in the industry, for a variety of reasons. One important reason for this is that unlike other types of tape cartridges which have been developed for use in the off-line storage of data, the IBM 3480 tape cartridge houses only a single reel of magnetic recording tape in a relatively small, space-efficient package. The resulting package is therefore conveniently stored and easily used.
To this end, the leader block which is connected to the free end of the web of tape is used to introduce the web of tape to the transport apparatus (and the read/write head). The transport apparatus must therefore be provided with appropriate means for withdrawing the leader block from its nesting within the 3480 tape cartridge, and for threading the leader block (and the web of tape) through the apparatus and past the read/write head. Of course, means must also be provided for unthreading the web of tape (and the leader block) from the apparatus, and for replacing the leader block within its nesting in the 3480 tape cartridge.
To this end, special means must be provided to engage the leader block assembly, and to guide the leader block (and the tape which follows) through the transport apparatus which is to operate upon the web of tape. This requires care in withdrawing the leader block from the tape cartridge, and in guiding the web of tape from the supply reel of the tape cartridge, past the read/write head, and into engagement with the take-up reel which is traditionally provided to cooperate with the supply reel in transporting the web of tape through the apparatus and past the read/write head. This necessitates the development of an appropriate path for threading the leader block through the apparatus, as well as means which have sufficient driving forces to withdraw the leader block from its normally seated position within the tape cartridge, and to replace the leader block within this normally seated position after the tape cartridge has been used. To meet these needs, as well as other design requirements regarding data density and performance characteristics, those devices described in the above-identified United States patents each make use of a leader block loading mechanism which is operated by a relatively large, dedicated driving motor, leading to significant demands for space and power, and overall cost.
Yet another consideration is that, as with any magnetic tape recording apparatus, care must be taken to develop a proper tape path between the supply and take-up reels, and across the read/write head, to assure proper registration of the tape with the read/write head. To this end, those devices described in the above-identified patents each provide a tape path of significant length, to account for such potential irregularities. Also to be considered in this regard is that care must be taken to avoid undesirable contact between the oxide coating provided on the web of magnetic recording tape and components such as bearings and idler rollers.
As a result of these and other design considerations, those devices which were originally developed to operate upon the 3480 tape cartridge were relatively large, cumbersome and expensive. While this was justifiable in connection with relatively large, mainframe computer applications, such design constraints tended to limit, and at times even preclude use of the 3480 tape cartridge in connection with lower cost, minicomputer or microcomputer applications. Yet another limiting factor was that of space. It was generally impractical, and therefore undesirable, to necessitate the purchase of an apparatus for off-line, back-up storage or the like which was significantly larger than the primary equipment which the apparatus was to support.
In fact, due to the prevalent use of both 8 inch and 51/4 inch magnetic recording (floppy) discs in connection with such applications, de facto standards arose for any form of storage equipment (floppy disc, hard disc, cartridge, etc.) which would replace or otherwise relate to such conventional storage means. The recognized "form factor" or "footprint" of a standard 8 inch magnetic recording disc calls for a container or housing having dimensions on the order of 8.5 inches in width, 15 inches in depth and 5 inches in height. The recognized "form factor" or "footprint" of a standard 51/4 inch magnetic recording disc calls for a container or housing having dimensions on the order of 53/4 inches in width, 8 inches in depth and 31/4 inches in height. Those devices described in the above-identified patents were not adaptable to such applications, limiting the ability to use the 3480 tape cartridge in mini/micro-computer applications.
Recognizing this, efforts were made to develop tape transports which were capable of operating upon a 3480 tape cartridge, and which were also capable of being contained within the reduced form factors or footprints required in connection with conventional mini/micro computer systems. One example of this is the "Patriot" tape transport which is manufactured by Computer Peripherals Inc., of Norristown, Pa., which incorporates a modified tape path adapted to provide all of the functions necessary to properly interface a 3480 tape cartridge with a tape transport, in a housing which is sufficiently small to accommodate a 51/4 form factor. However, this and other devices which have been developed for this purpose have generally required a compromise between the overall size of the transport, and its overall performance, particularly in terms of the data transfer rates which could be achieved in connection with such systems. Accordingly, while providing adequate results in connection with relatively low performance systems, it was found that this compromise tended to limit the utility of such transport devices for larger systems.
It therefore became desirable to develop a transport apparatus capable of accommodating the reduced form factors or footprints needed for conventional mini/micro computer applications, yet which could provide the higher performance characteristics which were necessary to satisfy the ever-expanding computer technology, and which was capable of operating upon data in the same format (parallel track, high transfer rate) as that used by the IBM Corporation in connection with its 3480 tape cartridge systems, to promote interchangeability with other systems.